1. Field of the Invention
The present invention relates to optoelectronic apparatus, for example to signal interconnections between the electronics and the optical transmission medium and vice versa.
Advanced systems for long distance and short distance communication need very high speed interconnects for the inter system as well as intra system information transmission. The standard technology for this purpose is optical transmission over fibers. The key components for the aforementioned technology include the electro-optic (e-o) transducer acting as a transmitter, and the opto-electronic (o-e) transducer acting as a receiver. Such transducers are used in every optical communication system.
For the very high transmission speeds of 10 Gbit/sec and above it is necessary to apply high speed optical and electronic components as well as special solutions for the packaging of such a transducer module in order to reach the required overall high-frequency (HF) performance.
A transmitter or receiver module in general consists of the module housing with an electronic interface and an optical interface and the opto-electronic assembly inside the housing. The opto-electronic assembly consists of an arrangement of: 1) optical components such as laser diode and photodiode chips; 2) active electronic components such as patterned circuit boards and mounted integrated circuits; and 3) other mechanical or passive optical components, wherein all components are inside the housing.
To achieve good HF-performance with such an opto-electronic assembly it is necessary to use a circuit board with impedance matched electrical transmission lines as well as an assembly and interconnection technology that is optimized for the high speed signal transmission. Furthermore, the opto-electronic assembly has to comply with the type and performance specifications of the applied optical and electronic components.
Such opto-electronic assemblies are used inside packages that include an optical and an electronic interface (or port). The optical interface of such a package is attached to an optical connector or optical fiber port and forms what is called a subassembly. The subassemblies with an optical connector for departing or entering optical data signals are called transmitter optical subassemblies (TOSAs) and receiver optical subassemblies (ROSAs), respectively. Such subassemblies are used as a building block in higher complexity integrated modules such as various types of transceivers or transponders that include a TOSA and a ROSA and also various kinds of electronic functions via an electronic port. For these types of applications there is limited physical space and it is necessary that the package is designed in a geometry wherein the optical port and the electronic port are located on opposite sides of the package.
2. Description of Prior Art
The prior art opto-electronic transducer modules for high speeds like 40 Gbit/sec use as the optical transducer edge-emitting or edge-receiving semiconductor chip devices (see FIG. 1). These devices are assembled in a planar arrangement in order to achieve the desired HF-performance. The devices are arranged parallel to the surface of the circuit board (100). The laser diode (110) is assembled on a submount (120) in order to reach a similar height as the top surface of the circuit board (100), and the main optical axis of the optical radiation is also parallel to the surface of the circuit board.
In a further arrangement the edge-emitting laser or edge-sensitive photodiode (PD) is mounted upside down using the “Flip-Chip” assembly method directly on the top surface of the circuit board. This results in superior HF-performance because the electrical connections are very short.